Nickel particularly has an excellent corrosion resistance in alkali, and also has corrosion resistance even in a high-concentration chloride environment. Therefore, it has been used as a member for use in various chemical plants including facilities for producing caustic soda, vinyl chloride and so on.
The above-mentioned members include a seamless pipe, a welded pipe, a plate, an elbow and so on. In apparatus and devices used in the said facilities, a member made of nickel (hereinafter also referred to as a “nickel material”) is often used in a welded state.
Carbon is contained as an impurity element in the nickel, however, the solubility limit of carbon in the nickel is low. Therefore, a long period of the use of nickel material at a high temperature may cause precipitation of carbon on the grain boundaries, or the welded nickel material may cause precipitation of carbon on the grain boundaries because of the heat affect on the occasion of welding; in both cases, the nickel material becomes brittle, therefore the mechanical properties and/or corrosion resistance thereof may be deteriorated.
Accordingly, in the JIS H 4552 (2000) for “Nickel and nickel alloy seamless pipes and tubes”, the carbon content of the nickel material having an ordinary carbon level (alloy number: NW2200) is prescribed to be not more than 0.15%. On the other hand, the carbon content of the nickel material having a low carbon level (alloy number: NW2201) is prescribed to be not more than 0.02%. As mentioned above, in the fields of application involving use at a high temperature, the nickel material reduced in the carbon content from the ordinary level to a level of not more than 0.02% has been put to practical use.
However, even in the case of a nickel material in which the content of carbon has been reduced to a low level of not more than 0.02%, during a long period of use at a high temperature, carbon which is contained in the nickel as an impurity mainly precipitates on the grain boundaries, and thus the said precipitated carbon has a malignant influence on the corrosion resistance, mechanical properties and so on.
As for the nickel materials, for example, various techniques have been proposed in the Patent Documents 1 to 4.
That is to say, the Patent Document 1 discloses an “improved nickel anode” for the use of nickel plating, which contains 0.1 to 0.5% of carbon and 0.1 to 1% of titanium in pure Ni. According to this technique, as the result of the addition of titanium, which has a strong affinity for carbon, the said titanium reacts with carbon during the dissolution of the anode in the plating solutions, and a thin film of TiC is formed. The said thin TiC film inhibits nickel particles from disintegrating and falling, whereby fine and shiny plating can be attained.
The Patent Document 2 discloses a “Ni alloy having high hardness and low contact electric resistance” which contains, on a weight percent basis, C: 0.05 to 0.3% and Mo: not more than 8% and/or Nb: not more than 5.5% provided that 3.1×Nb+Mo is 7 to 17%. In this Patent Document, it is mentioned that the Nb precipitates as Nb carbides, and the said carbides harden Ni.
The Patent Document 3 discloses a “Ni base alloy for boronizing treatment” which contains at least one element selected from Ti, Nb, Si, Zr, Hf, Mo and Ta in respectively specified amounts. The said ally is to be subjected to boronizing treatment in order to form a very hard boride layer.
Further, the Patent Document 4 discloses a “high-purity nickel core wire for inert gas shielded arc welding” which has the composition of Ni≧99%, C≦0.02%, Ti+Al: 0.1 to 1.0% and O (oxygen)≦0.002% in order to prevent the occurrence of weld defects such as cracks and blow holes.
Patent Document 1: Japanese Examined Patent Publication No. 36-14006
Patent Document 2: Japanese Unexamined Patent Publication No. 02-236250
Patent Document 3: Japanese Unexamined Patent Publication No. 62-250141
Patent Document 4: Japanese Examined Patent Publication No. 44-10654